The problem with many endurance sports is that even when given unlimited access to fluid, dehydration still occurs. Exercise performed for more than one hour in a hot/humid environment can result in a loss in excess of 3 liters of body fluid. Even when water consumption is increased in an effort to hyper-hydrate, the kidneys remove most of it within the hour. That’s where glycerol comes in.

Robert Robergs at the University of New Mexico reports that adding glycerol to water can prolong the time before dehydration by up to four hours. Intriguingly the mechanism in which glycerol achieves this effect is not clear. Reports show no reduction in body core temperature nor is there any increase in plasma volume. A study performed by Robergs and colleagues at this university showed a protocol that provided the greatest hyper-hydration. It involved starting glycerol ingestion 2 ½ hours before the event.